The cytochromes P-450 of lung, liver and epithelial tissue are known to play a central role in carcinogen activation, drug and xenobiotic detoxification and steroid and prostaglandin metabolism. The glass of this program have been to elucidate the organic and inorganic chemistry of the processes mediated by cytochrome P-450 referred to collectively as oxygen activation and substrate oxygenation. Our two-pronged approach has been (i) to employ substrates for cytochrome P-450 designed to reveal the nature of unseen intermediates and (ii) to develop model systems as chemical paradigms for these processes. An important aspect of these studies has been the direct comparison of enzymic and model reactions in the same laboratory. In the proposal that follows experiments are described which bear on the following specific goals: (1) To continue the preparation and characterization of highly oxidized iron porphyrin intermediates. (2) To develop low temperature electrochemical techniques for the direct measurement of redox potentials of oxidized iron porphyrins. (3) To study the mechanisms of 0-0 bond cleavage mediated by iron porphyrins. (4) To continue our study of the mechanisms of substrate oxygenation by oxidized iron porphyrins. (5) To understand the unprecedented hydrogen-deuterium exchange that accompanies the epoxidation of propylene by cytochrome P-450LM. (6) To explore the glycol cleavage reaction cytochrome P-450scc and the ethanol oxidation of cytochrome P-450LM3. (7) To study the oxidase activity we have found for mangano-horseradish peroxidase. (8) To extend the chemistry of cytochrome P-450 toward a general understanding of oxygen metabolism in biology.